Cranes are used for heavy lifting, but weigh several tons (since they typically use heavy counterweights) and typically are stationary, with a predefined range or so-called ‘reach.’ Some cranes are mounted on wheels, thus rendering them tow-able or even drivable, but they still suffer from the same weight and reach problems. Moreover, cranes are very expensive to own and operate. Forklifts have the same problems of high weight and cost, and suffer even more limited reach relative to their counterweighted base, but they are maneuverable. Neither cranes nor forklifts are lightweight and portable enough to be employed in rooftop installations.
Auto shop engine pullers use hoists, e.g. cable and pulley systems, or hydraulics to meet medium load lifting needs. They are generally fixed in position and do not break down easily for transporting to a different work site. Moreover, such an engine puller typically has a negative range, i.e. its effective lift range is within the perimeter of its base's footprint.
Rooftop installations, e.g. of heating/ventilation/air conditioning/refrigeration (HVAC/R), often require lifting of light to medium loads of less than approximately 1000 pounds. It is most often cost-prohibitive to do a rooftop installation or replacement, e.g. of an air conditioning unit, using a crane. A typical shop forklift weighs upwards of twelve tons, exceeding the load capacity of most rooftops. In any event, a crane would typically be required to lift the forklift onto the rooftop. Hydraulic/pneumatic lifts are heavy and difficult to transport. Moreover, a hydraulic/pneumatic lift requires power and/or a hydraulic/pneumatic source.